Terraform doesn't understand pre-release required_version constraint

[marshall7m]

Terraform Version

0.15.0-beta2

Terraform Configuration Files

terraform
terraform {
  required_version = "0.15.0-beta2"
}

output "test" {
    value = "foo"
}

Debug Output

Crash Output

Expected Behavior

Outputs:

test = "foo"

Actual Behavior

│ Error: Unsupported Terraform Core version
│ 
│   on main.tf line 2, in terraform:
│    2:   required_version = "0.15.0-beta2"
│ 
│ This configuration does not support Terraform version 0.15.0-beta2. To proceed, either choose
│ another supported Terraform version or update this version constraint. Version constraints are
│ normally set for good reason, so updating the constraint may lead to other errors or unexpected
│ behavior.

Steps to Reproduce

1. `terraform apply

Additional Context

Using tfenv for Terraform version management. Specifically using tfenv use 0.15.0-beta2 before running terraform apply

References

[alisdair]

Hi @marshall7m, thanks for reporting this. I can see this behaviour too.

This is caused by the version package initializing the SemVer variable without the Prerelease field. I think we should be able to update that, but there may be some reason why we don't support constraints against the prerelease field that I'm not aware of.

[alisdair]

An update after a failed attempt to fix this: while the issue is at root caused by this mismatched SemVer value, this is too load bearing to change. Instead I think we should try updating the specific location where we check the Terraform version against the constraints, and use the prerelease only in that spot.

[marshall7m]

thanks @alisdair for taking a look at this. I'm not too familiar with the internal aspects of Terraform (and Go in general) but it seems like your PR will fix it. Thanks!

[marshall7m]

I don't know if this helps or brings up another issue but when I use required_version = "0.15.0" within all modules used within the target Terraform configuration, Terraform doesn't raise a version constraint error when I use Terraform version 0.15.0-beta2.

[bflad]

FYI, this also happens when locally installing Terraform CLI. For example, terraform version and the version error will output 1.0.11-dev but the constraint must be 1.0.11.

[alisdair]

I just reinvestigated implementing the second idea I had posted above, and it's also a non-starter. If we consider the full version (including prerelease) when calculating required_version compliance, modules with constraints like >= 0.12.0 will fail with any prerelease version.

This is because go-version rejects prerelease versions for constraints which use inequality checks. Making the change I suggested would break the use of modules with any prerelease build.

At the risk of being wrong for the third time in a row, I think the only useful thing we can do here is warn or error if the required_version field contains a prerelease version number.

[bflad]

That sounds reasonable to me 👍

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